The present invention relates to the field of motor vehicle safety, and more particularly concerns a hybrid gas generator which includes an initiator with shaped explosive charge and is intended to inflate an airbag for the occupant of a motor vehicle.
In order to minimize the risk of body injury suffered by the occupants of a motor vehicle in the event of a front or side impact, it was proposed thirty years ago to fit motor vehicles with gas generator systems for inflating front or side airbags.
Many of these generators are hybrid gas generators which have the feature of inflating the airbags through the release of a gas contained until then under pressure in a leaktight container, it also being possible to mix this gas with other gases resulting from the combustion of an associated pyrotechnic charge. These hybrid gas generators, which have been the subject of various patents, for example U.S. Pat. No. 5,602,361 and U.S. Pat. No. 5,131,680, generally have a mechanical component for releasing the gas held under pressure in the container which, at the appropriate time, tears a diaphragm or destroys a wall which had hitherto closed the container in a leaktight fashion. This mechanical release component is, for example, formed using a metal projector that can be propelled by a pyrotechnic effect. Unfortunately, there are genuine disadvantages with hybrid gas generators equipped with such mechanical release components. Specifically, the relatively large number of difficult-to-machine metal parts which are needed for producing such components give these generators, on the one hand, high manufacturing costs, which is a problem in a highly competitive market such as that of motor vehicle safety and, on the other hand, significant weight and bulk.
It has therefore been proposed, as described in U.S. Pat. No. 5,263,740, to replace this mechanical release component by an initiator with shaped pyrotechnic charge placed in contact with the diaphragm that closes the gas container in a leaktight fashion. The result of this is, however, on the one hand that the cold gas contained in the container is forced to pass through the initiator when the latter has torn the diaphragm, which has the effect of heating this gas so that it may then damage the airbag still folded around the generator and, on the other hand, that it is very difficult to accommodate an associated pyrotechnic charge, intended to be initiated using the initiator with shaped pyrotechnic charge, elsewhere than inside the container.
The person skilled in the art is therefore still trying to find an inexpensive hybrid gas generator with low weight and bulk which makes it possible to release cold gases as soon as the generator starts to operate, which can also contain an associated pyrotechnic charge accommodated outside or inside the container, and makes it possible to inflate both front airbags and side airbags.
The specific object of the present invention is to provide such a hybrid generator.
The invention therefore relates to a hybrid gas generator comprising a container having an open end in which a compartment, which is located outside the said container and is provided with gas discharge orifices, is fixed, the said compartment containing an igniting system and having an openable wall which initially makes it possible to separate the inside of the container from the inside of the compartment, in a leaktight fashion, the said container holding at least one gas under pressure, characterized in that the igniting system consists of an initiator with shaped explosive charge capable of destroying the openable wall of the said compartment from a distance.
Thus, by virtue of the presence in the generator of an initiator which, during operation, can deliver a shot consisting of a plasma for perforating the said wall of the compartment from a distance, the cold gas contained in the container is released into the compartment and can then escape directly through the gas discharge orifices and inflate the airbag, without having to undergo direct contact with the initiator.
Preferably, the container and the compartment are of cylindrical general shape, the axis of revolution of the said container and the axis of revolution of the said compartment being the same, and the initiator with shaped explosive charge is located on the same axis. The compartment may be made from a cylindrical hollow body having a side wall in which there are gas discharge orifices, a front wall in which there is an opening initially closed by a diaphragm, and an open end in which a closing ring, supporting the initiator with shaped explosive charge, is fixed.
Advantageously, the initiator with shaped explosive charge is an electrical initiator containing, on the one hand, a starting pyrotechnic composition relayed by a relay primary explosive and, on the other hand, a composite explosive comprising at least one binder and at least one nitramine, the said composite explosive being shaped in the form of a hollow charge. This relay primary explosive consists, for example, of penthrite or silver nitride and makes it possible to initiate the composite explosive forming the shaped charge. This type of initiator is highly effective in delivering a shot having a highly extended field of action.
According to a first alternative embodiment of the invention, the compartment may accommodate an associated pyrotechnic charge. This pyrotechnic charge is ignited using the initiator with shaped explosive charge and makes it possible, once some of the cold gas delivered from the compartment has initiated inflation of the airbag, to generate gases which mix with the cold gas in order to deploy the airbag fully.
Preferably, the associated pyrotechnic charge is in the form of an annular block arranged around the initiator with shaped explosive charge. Also preferably, the compartment has an internal partition provided with an opening closed by a diaphragm, the said internal partition making it possible to divide the said compartment into a first chamber for initiation and combustion containing the initiator with shaped explosive charge as well as the pyrotechnic charge, and a second chamber for mixing and discharging the gases which includes the openable wall and the gas discharge orifices.
Advantageously, the initiator with shaped explosive charge is formed using:
i) an igniting medium,
ii) a fragmentable cap having a hollowed bottom, a side wall and an open end fixed on the igniting medium, the said cap containing at least one explosive composition based on nitramine and the said side wall having at least one weakened zone,
iii) and an electrical initiation system connecting the igniting medium to a current source.
This initiator, which makes it possible to deliver a shot intended to break the openable wall of the compartment in order to release the cold gas contained in the container, thus also has a lateral weakened zone whose destruction during operation allows the gases generated by the initiator to come into contact with the associated pyrotechnic charge. This is particularly advantageous when the latter is in the form of an annular block arranged around the initiator.
Preferably, the fragmentable cap contains a reinforcing powder interposed between the open end of the cap and the explosive composition which is in contact with the hollowed bottom in a manner such that the said reinforcing powder is arranged in front of the weakened zone, it being possible for the latter to consist of a narrowed peripheral band of the side wall of the cap or of orifices in the said side wall which are closed by diaphragms. Also preferably, this reinforcing powder will be mixed with the relay primary explosive.
Advantageously, the igniting medium consists of an insulating medium on which a resistive heating element as well as the starting pyrotechnic composition are deposited, it being possible for the said resistive heating element to consist, for example, of a semiconductor bridge or a resistor wire which is connected to a current source using two pins which conduct the electric current, constituting the electrical initiation system.
According to a second alternative embodiment of the invention, an associated pyrotechnic charge may be accommodated in the container and arranged in front of the openable wall of the compartment. This pyrotechnic charge is ignited using the shot delivered by the initiator with shaped explosive charge and makes it possible, once some of the cold gas delivered from the compartment has initiated inflation of the airbag, to generate gases which mix with the cold gas in order to deploy the airbag fully.
Preferably, the pyrotechnic charge is placed inside a cup having a flat circular bottom and a side wall whose free end is fixed in the compartment.
Also preferably, the flat circular bottom has a central hole closed by a diaphragm, and the pyrotechnic charge, on the one hand, is wedged by a separating ring fixed in the side wall of the cup and, on the other hand, surrounds a starting relay device which rests on a profiled central orifice of the said separating ring.
Advantageously, the side wall of the cup has communicating orifices between its free end and the separating ring.
The invention also relates to an electro-pyrotechnic initiator comprising, in particular, an igniting medium in which the open end of a fragmentable cap containing at least one explosive composition is fixed, and an initiation system which makes it possible to connect the said igniting medium to an electric current source, characterized in that
i) the fragmentable cap has a hollowed bottom whose inner surface is in contact with the explosive composition,
ii) the cap has a side wall including at least one weakened zone.
According to a first alternative embodiment of the invention, the cap contains a reinforcing powder interposed between the open end of the cap and the explosive composition in a manner such that the reinforcing powder is arranged in front of the weakened zone.
According to a second alternative embodiment of the invention, the explosive composition consists of a composite explosive containing at least one binder and at least one nitramine. Advantageously, the cap contains a relay primary explosive. This relay primary explosive is advantageously mixed with a reinforcing powder, and this mixture is interposed between the open end of the cap and the explosive composition, so as to be arranged in front of the weakened zone.
Preferably, the weakened zone consists of a narrowed peripheral band of the side wall of the cap, or alternatively of orifices in the said side wall which are closed by diaphragms.
Advantageously, the diameter of the cap is at least equal to 8 mm, and the bottom is hollowed in the shape of a cone, the latter having a vertex angle at most equal to 30xc2x0.
Also advantageously, the igniting medium consists of an insulating medium on which a resistive heating element as well as a starting pyrotechnic composition are deposited, it being possible for the said resistive heating element to consist, for example, of a semiconductor bridge or a resistor wire arranged in contact with the starting pyrotechnic composition, and to be connected to an electric current source using an initiation system including two conductive pins. The initiation system may also consist of an optical cable combined with a laser device.
A hybrid gas generator according to the invention therefore provides a solution to the problem set out above, since:
it does not require a mechanical component for releasing the gases,
it allows the cold gas contained in the container to initiate the inflation of the airbag by virtue of opening the said container from a distance,
it can contain an associated pyrotechnic charge that generates gas, both in the compartment and in the container,
it makes it possible to inflate a side airbag of small volume, it then being possible for the gas source needed to inflate the bag to come exclusively from the gas contained under pressure in the container.